.focus {
    overflow: hidden;
    position: relative;
    float: left;
    width: 721px;
    height: 455px;
    cursor: pointer;
}


/* 因为focus 盒子不够宽，小li浮动不了，所以给ul添加足够宽的宽度，让小li浮动起来 */

.focus_ul {
    position: absolute;
    top: 0;
    left: 0;
    width: 900%;
}

.focus_ul li {
    float: left;
}

.focus_f,
.focus_r {
    display: none;
    position: absolute;
    top: 50%;
    transform: translateY(-50%);
    width: 30px;
    height: 40px;
    background-color: rgba(0, 0, 0, .2);
}

.focus_f {
    left: 0;
    border-top-right-radius: 25px;
    border-bottom-right-radius: 25px;
}

.focus_r {
    right: 0;
    border-top-left-radius: 25px;
    border-bottom-left-radius: 25px;
}

.focus_f::after,
.focus_r::after {
    content: '';
    position: absolute;
    top: 15px;
    width: 8px;
    height: 8px;
    border-top: 2px solid rgba(255, 255, 255, .8);
    border-right: 2px solid rgba(255, 255, 255, .8);
}

.focus_f::after {
    left: 10px;
    transform: rotate(225deg);
}

.focus_r::after {
    right: 10px;
    transform: rotate(45deg);
}

.focus_b {
    position: absolute;
    left: 40px;
    bottom: 20px;
    height: 16px;
}

.focus_b .border {
    border: 3px solid rgba(0, 0, 0, .3);
    background-color: #fff;
    margin: 0;
}

.focus_b ul li {
    float: left;
    width: 10px;
    height: 10px;
    margin: 3px 3px;
    border-radius: 50%;
    background-color: rgba(255, 255, 255, .4);
    border: 0.5px solid rgba(0, 0, 0, .05);
    box-sizing: content-box;
}